The natural occurrence of secondary bacterial symbionts in aphids

Abstract

Abstract. 1. Many insects host secondary bacterial symbionts that are known to have wide-ranging effects on their hosts, from host-plant use to resistance against natural enemies. This has been most widely studied in aphids, which have become a model system to study insect-bacteria interactions.2. While there is an increasing understanding of the role of symbionts in aphids from controlled laboratory studies, we are only beginning to explore the impact of hosting these symbionts on eco-evolutionary dynamics in natural systems. To date, many research groups have identified bacterial symbionts from various aphid species, providing us with a bank of literature on aphid-symbiont associations in natural populations.3. The role of secondary symbionts in aphids is discussed, and the taxonomic and geographical distribution of symbionts among aphids are summarised, and the potential reasons for the patterns observed. The need to test for multiple symbiont species (and co-infections) across many individuals and the whole distribution range of an aphid is highlighted, including sampling on all known host-plant species.4. It is further important also to consider variation within the symbiont, the aphid-host and the surrounding community, e.g. host-plants or the natural enemies, to understand how these have the potential to mediate aphid-symbiont interactions.5. Finally, the knowledge gained from experimental work should now be used to understand the role of aphid secondary symbionts in field systems, to fully understand the potentially far-reaching consequences of aphid endosymbionts on community and ecosystem processes.

Are aphid parasitoids locally adapted to the prevalence of defensive symbionts in their hosts?

“…This matches observations from pea aphids, in which multiple reproductively isolated host races differ strongly in the relative frequencies of infection with different facultative endosymbionts [57, 58]. There is increasing evidence that such differences are adaptive [59–61], and it will be interesting to determine the main selective forces shaping these symbiont communities. By using diagnostic PCR, we could only detect symbionts we screened for, hence our study cannot provide a comprehensive picture of the complete symbiont community in these aphid species.…”

Wolbachia dominate Spiroplasma in the co‐infected spider mite Tetranychus truncatus

“…Symbiont co‐infections are common in arthropods, such as spider mites, aphids and grasshoppers (Machtelinckx et al ., ; Lukasik et al ., ; Wamwiri et al ., ; Funkhouser‐Jones et al ., ; Moutailler et al ., ; Zhang et al ., ; Zytynska and Weisser, ; Nguyen et al ., ). The presence of co‐infections in mites and other arthropods raises questions about how such infections are generally maintained.…”

Cohabitation and roommate bias of symbiotic bacteria in insect hosts

“…than alfalfa ( M. sativa ). Consistent associations across the data set included a negative association between H. defensa and R. insecticola and a positive one between H. defensa and X‐type (previously identified, reviewed in Mathé‐Hubert et al, ; Zytynska & Weisser, ). The majority of negative associations occurred among the more abundant symbionts, leading to a negative correlation between the prevalence of a particular symbiont and the number of coinfecting symbionts to be greater than expected under random assortment.…”

“…Interactions with symbiotic bacteria can also benefit aphid survival and population growth. However, only 40%–60% of aphids in a population are infected by even the most prevalent secondary symbiont (Zytynska & Weisser, ) indicating that there must be some way in which host aphids lose and gain symbionts. Aphid symbionts are predominantly vertically transmitted from mother to offspring during reproduction, with transmission failure rates ranging from 0% up to 40% in the field depending on the symbiont species, other hosted symbionts, and host genotype (Rock et al, ).…”